DE1960814C3 - Device for grinding twist drill tips - Google Patents

Description

The invention relates to a device for grinding twist drill tips according to the preamble of Claim 1.

From US-PS 32 09 493 a device of the generic type is known, however, conical for grinding drill bits used to drill held in a drill holder is delivered by a cam drive to a conical peripheral grinding surface of a grinding wheel and brought from this again ^r> disengaged

In contrast, the invention relates to a device for grinding convexly curved Drill bits. The generatrix of convex curved drill tips is curved by a

ίο line marked, usually by an arc, which is struck in a plane through the longitudinal axis of the drill from a center point, the is arranged either on or next to the longitudinal axis of the drill. This arc can be tangential to the

H the drill shank or its guide chamfers run in, advantageously, however, the arc does not quite reach the point of connection with the guide bevel tangential direction. On the other hand, the arc merges with the tip advantageously with the interposition of the connection a frustoconical section. The drill tip has the usual cross cutting edge or a Modification of this on.

Such a drill bit requires a deviation from the aforementioned rotational surface by one To ensure cutting edge clearance angle or an undercut behind the cutting edge, which follows is referred to as an axial relief. Because the curved cutting edge along its entire length cuts, / on the cross-cutting edge to the point where

If it runs into the guide chamfer of the drill, the free surface must also have a radial relief. This means that the curved flank behind the curved cutting edge with a clearance angle must be ground, which appears in a plane at right angles to the drill. Drill tips this general Art are described in US-PS 13 09 706 and 34 43 459.

Such drills have certain advantages in some special materials or in special applications. The drill bits are made by skilled workers using a suitable abrasive sanded. The grinding process, however, requires a highly skilled worker, and it is close to impossible to achieve a really precisely curved drill bit by such a hand grinding process. Grinding machines for producing such drill bits have recently become known. These are hand operated Machines that perform successive grinding operations against a flat grinding wheel surface are executed.

The object of the present invention is to produce the grinding device mentioned at the beginning of convex curved drill tips of high precision.

This object is achieved according to the invention with a device for grinding twist drill tips solved according to the characterizing part of claim 1.

The device according to the invention basically matches the drill bit grinding device of US-PS 32 09 493 match. For grinding convexly curved drill tips as opposed to conical ones However, drill bits must have a novel movement sequence of the drill in relation to the grinding wheel can be provided, which movement sequence by changed profile and mutual displacement of the Cam is achieved. In addition, the grinding wheel has a novel contour of a peripheral grinding surface

9 60814

to train. A device modified in this way allows the production of higher quality convex curved precision drill tips.

A grinding wheel with a concavely curved circumferential grinding surface is used in a drill bit grinding machine according to US-PS 21 24 093 used This grinding wheel is used to form chamfers at the corners of otherwise conical ground drill tips.

The invention is explained in more detail below with reference to drawings. It shows

F i g. 1 slide schematic perspective view a device according to the invention for grinding twist drill tips;

F i g. Fig. 2 is a line diagram relating to the drill movement;

Fig. 3, 4 and 5 are schematic on a larger scale Partial views showing successive positions of the drill in relation to the grinding wheel and

F i g. 6 and 7 show a side view and a perspektivi- m see view of a convex curved drill fungi.

A twist drill provided with two flutes is shown in FIG. 6 and 7 and denoted by d. This has a shank s with a raised guide bevel m , and it is provided with a point ρ, which has a cross cutting edge c and curved cutting edges r, behind which open areas 1 are arranged. The drill tip is generally determined by a surface of revolution whose generatrix is an arc of a circle in a diametral plane of the drill, the cp about a center point is beaten (3 to FIG. 5), which is usually seillich offset of the longitudinal axis of the drill, the radius R this arch can e.g. B. take a value between 0.4 (or less) and about 0.75 (or more) of the drill diameter π. The tip has two cutting edges r, each of which is contained in the surface of revolution and the profile of which begins at the cross cutting edge with a straight section which runs into an arcuate section (around the center point cp of a curved section y of the grinding wheel), the arcuate section to is continued at a connection point in which this section preferably does not run completely tangentially into the front edge of the guide bevel m , as best shown in FIG. 3 can be seen. The grinding is done along the cutting edge of the chisel edge to the point m \ where the cutting edge runs into the guide land.

In Fig. 1, a grinding wheel with a profiled Umiangsschleiffläche 11 is shown at 10. The grinding wheel is rotatably arranged about a vertical axis AA on a drive shaft 12, preferably in a device which allows fine horizontal adjustment of its position in directions towards and away from the drill bit to be sharpened, as indicated by the double arrow A. The longitudinal axis DD 'of the drill 13 is essentially horizontal, but advantageously inclined slightly upwards, about 10 ° to the grinding wheel face. While this axis D-D 'can generally intersect the axis of the grinding wheel, it however advantageously deviates by a few degrees, about 2 to 4 ° from a straight connecting line between the drill and the wheel axis 4, 4', by the To support grinding in the axial relief grinding. The axis D-D 'extends to the left of the axis A-A' as seen from the drill.

The drill 13 is carried by a drill holder 18, which in turn is rotatably mounted in a support 20 about the drill axis. The support 20 is in Fig. 1 drawn broken away for the most part, and the bearings and the like are omitted in order to to be able to highlight the essential parts of the invention more clearly. The outer contour of the omitted parts is indicated in dash-dotted lines

The support 20 has a housing 22 on a column 24, the housing 22 projecting laterally from the column The column 24 consists of a vertical tube for performing an oscillating rotational movement about a vertical axis RB 'and performing an up and down movement along this axis BB 'is stored according the drill holder 18 is located at the extreme end of the laterally projecting housing 22, and oscillation of the column 24 oscillates the casing with the drill holder and the drill to the periphery and away from the periphery of the grinding wheel, while in the vertical up and down movement of the column 24 of the drill holder and the drill vertically in relation to the grinding wheel. These separate movements are carried out in such a way that the drill bit is lifted over the grinding wheel, then moved downwards into engagement with the concave peripheral grinding surface 11, after which, in one embodiment of the invention, it is moved downwards for a short distance against the surface 11 and then both downwards is also moved back laterally, ie along the contour of the surface 11. Finally, the drill tip is withdrawn from the surface 11. The contour of the grinding surface 11, which will be described in more detail later, and the sequence of movements of the drill bit in conjunction with a rotary movement of the drill about its longitudinal axis, produce the desired drill bit with high precision.

The rotation of the drill around its axis and the cyclic oscillating rotation, up and down movement of the column 24 are caused by an electric drive motor 30, which is at the lower end the column 24 is arranged. The drive shaft of this motor is, as shown in FIG. 1 can be seen on a vertical Drive shaft 32 coupled, which extends up through the column 24 into the housing 22, where it is over Bevel gears 34 and 35, a shaft 36 and a pair of gears 37, a worm wheel 38 drives which meshes with a worm wheel 39 on the rotatable drill holder 18. The latter thus becomes permanent rotated by motor 30.

The drive shaft 32 carries a worm wheel 40 which meshes with a worm wheel 42 a shaft 44 which is rotatable about its axis in bearings, not shown, arranged in the column 24 is stored. The shaft 42 carries two cam disks 46 and 48, the contour of which will be described later.

A cam follower wheel 50 is engaged with the cam plate 46 and is disposed on an arm of a crank 52 which is pivotally mounted on the column 24 via a shaft 54 to be able to oscillate about an axis which is parallel to the axis of the shaft 44 . The other arm of the crank 52 extends upwards and engages a support point 56 which, which is not shown, is attached to the machine frame. When the follower wheel 50 comes into engagement with the highest point of the cam plate 46, the crank 52 acts against the fixed support point 56 and a force is exerted via the shaft 54 which pivots the column about its axis BB ' against a yielding return spring 58. When the high point on the cam is below

the scanning wheel 50 moved through, the spring 58 moves the Column 24 back, so that the column is constantly through the interaction of cam plate 46 and return spring 58 about its axis ß-ß 'oscillated. Of course, the drill 13 oscillates in the holder 18 to Grinding wheel and away from the grinding wheel, alternately engaging with it and again is withdrawn.

The cam plate 48 is engaged with a follower wheel 60 on a lever 62 which is on a horizontal shaft 64 is mounted, the shaft parallel to the axis of the cams 46 and 48 runs and is stored in the column 24. The lever 62 acts on a support point 66, which on Machine frame is attached. When the highest point or range of the cam plate 48 comes into engagement with the scanning wheel 60, the lever 62 swings about the fixed support point 66 and thus lifts via the shaft 64 the column 24. The column descends after the high area of the cam disk has moved away from under the scanning wheel, due to its own weight. The drill holder and the drill are thus alternately raised and lowered relative to the grinding wheel.

The two cams ^ 46 and 48 are shaped and synchronized in such a way that those of them caused movements, pauses and timing coincide with the timing diagram of FIG. The actual strokes and pauses depend in each case on the design of the respective machine Diameter of the drill to be sharpened, the material to be drilled and the ideas of the user.

The description of the grinding wheel will now be discussed, the contour of the peripheral grinding surface 11 being described in detail. In the case specifically considered here, the profile of the concave grinding surface 11 consists of a line with a first frustoconical section x which assumes an angle t \ of about 20 ° to the vertical, a second concavely curved section v. into which the section λ runs tangentially and which is struck around the center point cp with a radius R. which in this particular example is larger than the radius of the drill bit to be sharpened, the section y sweeping an angle of about 54 °, and with a third frustoconical section z that runs tangentially into the lower end of the concavely curved section y and obliquely downwards radially outwardly directed with respect to the grinding wheel, at an angle of about 5 ° to 25 °, in the shown example at an angle of 6 to ^C drill shank or 16 ° to the horizontal. The advantageous angle can be obtained by the relationship (18Ö ^; - apex angle) / 2 -10 °, where in the present case where «. = 20 °, the point angle is 120 °. As mentioned above, the drill shank or its axis is preferably inclined at an angle of 10 ° to the horizontal. The center point cp of the curved grinding wheel section y is arranged next to the longitudinal axis of the drill, although this is not a condition and the center point cp can also be on the drill axis in modified designs.

From the diagram according to FIG. Z which is typical for a drill with two grooves of 6.3 mm diameter (shown in FIGS Drill holder 18, on the other hand, is such that the drill holder and the drill rotate 180 ° when the cams make a full 360 ° rotation. A 360 ° cycle of the cam disks is thus carried out for each of the two cutting edges r of the drill, ie the cam disks rotate once for half a revolution of the drill. In Figure 2, the lines Kund H mean the ordinates of the vertical or

κι horizontal movements of the drill over a Drill rotation of 180 °, and these ordinates represent the radii of the cam disks 46 and

48. distributed over 360 ° of cam disk rotation.

The sequence of movements as shown in the diagram

π F i g. 2 is as follows: Starting from one arbitrary reference point 0 ° in the diagram in which the drill is withdrawn and in its topmost position of vertical up and down movement is so that the drill bit is not in engagement with the grinding wheel is at a standstill, the drill moves to its foremost position over the first 60 ° of its rotary movement moved and is started at the same time with its vertical downward movement.

With a 60 ° drill rotation it comes in a straight line

? ^r ) line (at an angle a. to the grinding wheel section χ) downwardly moving drill bit in contact with a lower part of the grinding wheel section χ and with the curved section y, which corresponds to the position of FIG. The drill is in

so arranged in the drill holder that in this position an initial surface g of the free surface 1 of the drill tip, which is arranged adjacent the cutting edge / ", is in contact with the grinding surface. The surface g is dashed in Fig. 2 so that its general position

π can be seen. The cutting edge c on the drill mushroom is at this point about 30 "to the plane of the Inclined grinding wheel.

For the next 30 ° of the drill rotation, the drill is constantly in its advanced position

Leave 4Ii and is lowered at a very low speed, so that the somewhat lower position of Fig. 4 is reached, in which the drill mushroom is rotated by 30 "(second position in Fig. 2) and the cross cutting edge c extends horizontally, ie in one to the grinding wheel

* '■ · parallel plane. At this point in time, the surface g in contact with the grinding wheel has moved on a LIm circle over the free surface 1 in the middle position of FIG. 2 postponed. The cross cutting edge c is ground during this period of time, this

"■ <> The grinding process is completed at the end of this period of time. As a result of this vertical lowering of the drill and the essentially diagonal position of the grinding disk section χ with respect to the vertical, in conjunction with the rotation of the drill behind the

^ - Cutting edge ground an axial relief surface. The grinding of an axial relief surface is also made possible by the aforementioned arrangement of the Longitudinal axis of the drill laterally favors the axis of the grinding wheel. Thanks to the curvature of the

«· Grinding surface section y the axial relief is gradually reduced along the curvature in the direction of the drill shank. During this process, when the drill is lowered onto its tip, a radial relief surface is also ground, and

<* ■■ this radial relief becomes greatest at the lower part of the grinding section y, where it is most needed, and it progressively decreases in the direction of the drill tip, where it is less necessary. A

Comparison of FIGS. 3 and 4 shows that a certain radial undercut when lowering the drill from the position of F i g. 3 into that of F i g. 4 was generated. F i g. 3 and 4 illustrate this fact in that in FIG. 3 the drill is at a distance ν from the center point cp of the arc on the grinding wheel, while in FIG. 4 this distance has increased to ν + Δν. This means that in the position of FIG. 4 a radial relief, which was ground like Av'isl.

Starting from the last described position (central position of Fig. 2) the drill continues its steady but slow downward movement with a further 15 to 20 ° drill rotation, whereby the drill is withdrawn horizontally, i.e. it undergoes a downward movement, as in F. i g. 2, so that the drill tip detaches itself from the grinding wheel in the area of the cross cutting edge. The accentuating downward and outward movements are coordinated in such a way that, while the cross cutting edge is withdrawn from the grinding surface χ , the mushroom area under the loosened cross cutting edge continues to move downwards against the grinding wheel sections y and ζ. The section ζ of the grinding surface provided with a straight profile will grind a substantially frustoconical surface on the rear part h of the free surface 1 (FIG. 7). Thus, radial free space continues to be ground in the direction of the line of intersection with the shank. The in F i g. 5 position shown and the third position according to F i g. 2 is advantageously reached after 45 to 50 ° rotation of the drill, after the drill has come into contact with the grinding wheel for the first time. At this point in time, the surface g in engagement with the grinding wheel is only the radially outer, rearward area of the free surface. The drill has lowered itself in this position by an additional distance Δν ' , and its axis is now at a distance r + Δν + Δν' from the center point cp. In this way, a radial relief which is equal to Δν + Δν 'was created. From the position of FIG. 4 to the position of FIG. 5, the drill was also withdrawn horizontally by a short distance Δα. As an important point, it should be emphasized at this point that the drill tip was slightly withdrawn from the steeper part of the grinding surface so that the previously ground cross-cutting edge is not damaged again, while the desired radial undercut continues to be ground on the radially outward rear part of the flank of the drill will.

As soon as the drill bit comes out of engagement with the grinding wheel, it is removed from the grinding wheel withdrawn and raised again so that a new, identical grinding process can follow.

Let us now consider Figure 3, which shows the position in which the cutting edge r is in relation to the grinding wheel when it is first touched. It can be seen that the cutting edge r of the drill bit in the area of the cross cutting edge is partially ground by the straight grinding wheel section χ and partially by the curved section y. It can also be seen that the curved section y encloses an acute angle, here 6 °, with the drill shank at the connection point in which the straight section ζ tangentially enters the section y. The curvature ground onto the cutting edge r thus runs tangential to the section z, but a few degrees are missing for tangential entry into the drill shank. This is an important feature since the cutting characteristics of the drill deteriorate as soon as the cutting edge runs completely tangentially into the side or guide land of the drill shank.

It has been found that in some cases it can be advantageous to provide a piece of straight profile on the drill point starting from the point up to a point at which this piece runs tangentially into the curved part. This can be achieved simply by reducing the contour of the peripheral grinding surface in relation to the drill size or, of course, also by grinding a larger drill in relation to the contour of the peripheral grinding surface. Such a larger drill with the shank S ' is shown in dashed lines in FIGS. 3, 4 and 5, and it is easy to see that proportionally a larger piece of the straight profile is ground onto the drill tip than with a drill, which is smaller in relation to the grinding wheel profile. It can also be seen that the reverse case occurs when using a smaller drill with respect to the grinding wheel profile. In this case, the drill bit can immediately come into engagement with the curved grinding wheel portion y , so that the straight portion * is unnecessary. However, as described above, it is preferred to use all three sections λ when grinding the drill tip. κ and z.

A modification of the invention, which can occasionally be used if 7. B. the grinding away of the cross cutting edge during the last phase of the grinding process does not matter, consists in designing the cam disk 46 so that the first advanced position according to FIG. 3 about the second position according to FIG. 4 is maintained while the drill is further lowered to the third position shown in FIG. The drill is therefore only when it reaches the position according to FIG. 5 withdrawn horizontally.

For this purpose 3 sheets of drawings

Claims (3)

Patent claims: 1. Apparatus for grinding twist drill tips with a cross-cutting edge-forming open area, consisting of a rotationally drivable grinding wheel with a profiled peripheral grinding surface and a drill holder which can be rotatably driven for successive grinding of the open areas and which is mounted in a cam-controlled support, the cam drive of which is derived from the rotary drive of the drill holder and which arranges the drill axis transversely to the grinding wheel axis approximately in a plane containing the grinding wheel axis, the area of each cutting edge of the drill being adjustable against the circumferential grinding surface of the grinding wheel and each free surface parallel to the grinding wheel axis and then moving the drill back and forth by rotating and moving the drill is ground to and away from the grinding wheel axis, characterized in that for grinding in planes convexly shaped by the drill axis (D-D ') open spaces (1) Sc grinding disc (10) consists of two frustoconical sections (x, z) of different inclination, between which a transition piece with a concave surface (y) extends, the cross-section of which lines arcuate in cross-section run into the corresponding cone surface lines on both sides, and that the drill (13) during of the grinding process while maintaining a constant angle of inclination to the grinding wheel face by means of the cam control (48, 60, 46, 50) against the frustoconical section (x) of lesser conical inclination of the grinding wheel and against the concave surface (y) and then through the axis to the grinding wheel (A-A ') parallel movement against the frustoconical section (z) of greater conical inclination of the grinding wheel (10) can be moved. 2. Apparatus according to claim 1, characterized in that the cam control (48,60,46, 50) of the drill (13) first to the grinding wheel axis (A-A ') is movable and can be lowered in the advanced position to a cross cutting edge (c ) to grind on the frustoconical section (x) of the grinding wheel (10) with a lower taper, and that the cam control (48, 60, 46, 50) allows the drill to be retracted during the last part of the movement parallel to the grinding wheel axis when the flank area ( AJt which is at a distance from the transverse cutting edge and the cutting edge (rj ¹ ) rests against the frustoconical section (z) of greater taper inclination. 3. Apparatus according to claim 1 or 2, characterized in that the drill holder (18) the drill axis (D-D ') at a small angle to the connecting line between the drill (13) and the grinding wheel axis (AA ' Jan arranges.